The Process And Optimization Of Ecosystem Flood Regulation Service Flow In The Blue-green Space Of The Han River Basin

In recent years,with the increasing cross regional impact of climate change,flood regulation services in upstream ecosystems of river basins have an increasing impact on downstream decision-making in response to floods.Therefore,it is urgent to consider flood regulation in upstream and downstream systems throughout the entire river basin.The key to addressing this challenge is to fully understand the spatial flow of ecosystem flood regulation services across watersheds from upstream to downstream.This study takes the Han River Basin in China as the research area and quantitatively studies the spatial flow and accumulation of ecosystem flood regulation services from upstream to downstream at the basin and sub basin scales.It explores the laws of flood regulation service flow in the basin ecosystem,evaluates the risk of flood disasters in the basin,and proposes optimization strategies for the blue-green spatial layout of the basin based on the results,To provide reference for comprehensive and comprehensive response to upstream and downstream flood disaster risks throughout the entire watershed.(1)The total supply of flood control services in the Han River Basin ecosystem is262.95×10~8m~3,of which 64%is supplied by artificial reservoirs.The high supply areas are mainly located in the central part of the Han River basin.At different watershed scales,there are significant differences in the supply level of ecosystem flood control services in each sub watershed.The ecological system flood control service supply and supply density of the first level sub watersheds g and h where the Danjiangkou Reservoir is located are much higher than those of other watersheds,with 57.83×10~8m~3 and70.95×10~8m~3,providing a total of 48.98%of the ecosystem flood control services in the entire Han River basin.The local flood overflow in two first level sub basins g and h is 0,and the local flood overflow in seven second level sub basins is 0.These sub basins not only meet their own flood regulation service needs,but also provide additional regulation capabilities for their downstream ecosystems.In addition,nearly 90%of sub watershed units have flood overflows,and the response to flood risks in the downstream of the watershed heavily relies on flood regulation services in the upstream ecosystem.(2)The flood overflow path from upstream to downstream in the Han River Basin is generally consistent with the trend of the main and tributaries of the Han River themselves.The cumulative flood volume of the secondary sub basins l6 and h5 is 0.The Danjiangkou Reservoir within the sub basin h5 has strong flood control capabilities,which can intercept all accumulated floods from the upstream basin and protect its downstream sub basin from flood threats.There are a total of 7 primary sub watersheds that can obtain flood regulation services from the upstream ecosystem,among which i receives the largest flow of ecosystem flood regulation services from its upstream adjacent sub watershed,and sub watershed e receives the smallest flow of ecosystem flood regulation services from its adjacent sub watershed.The downstream sub basin m obtained the highest cumulative flood regulation service flow in the upstream,reaching212.81×10~8m~3。(3)From the perspective of adjacent accumulation and non-adjacent accumulation of service flows,most of the ecosystem flood regulation service flows in the first and second level sub basins come not only from their upstream adjacent areas,but also from non-adjacent areas.Moreover,the cumulative amount of flood regulation service flows in non-adjacent sub basins is much higher than that of adjacent sub basin units.The sub basin c located in the middle reaches of the basin provides ecosystem flood regulation services in non-adjacent sub basins,second only to the downstream sub basin m1,and is a key area connecting the upstream and downstream of the basin to play a joint flood regulation role.From the perspective of basin gradient accumulation of service flow,the basin gradient accumulation flow of ecosystem flood regulation service on the scale of primary and secondary sub basins shows exponential function growth.In the starting sub basin a and ending sub basin m of flood regulation service flow,the cumulative flow of flood regulation service flow in the secondary sub basin increases linearly.(4)There are 56 secondary sub basins within the Han River that are flooded,with all areas of sub basin k3 being flooded,with a total area of 7438.55 km~2.The high-risk area of flood and waterlogging is 9.9 km~2,mainly distributed in the sub basins k1 and m11 in the middle and lower reaches of the basin.The moderate risk area of floods is 123.51km~2,mainly distributed in sub basins k1,m7,and m11.The low risk area of floods is6193.01 km~2,widely distributed throughout the watershed.Taking the high-risk areas of floods as the target area,considering the spatial patterns of flood accumulation in the upstream and downstream as a whole,and from the perspective of ecological restoration in the blue-green space,implementing measures such as returning farmland to forests,grasslands,and wetlands,and strengthening the construction of urban blue-green infrastructure can effectively reduce the flood risk within the flow area.